Bhojana Kala Manthram

Eating food is a holy ritual, a yajna. It should not be performed during moments of anxiety or emotional tension. Food has to be considered as medicine for the illness of hunger and as the sustenance of life.
Eating food(offering prasadam to God inside) is considered as Yagnam, so we are supposed purify self, wear cloths, and sit as you are sitting while doing Yagnam. Before our meals we do not speak of physical food but continue to refer and remind ourselves of our goal of attaining the highest consciousness, to therefore remember that all around us is Brahman or the immanent (sarva vyapi) aspect of god and eventually we must realize and attain the transcendental (vishvotirrna) aspect of god too. These shlok actually sums up Vedanta. Veda meaning knowledge and Anta meaning end and therefore Vedanta means the highest knowledge.

There are few shlokas used by different followers, here are few widely used,
1. Bhojana Shlokam from Annapurna stotram written by Sri Adi Shankracharya
Annapurna Sada Purne
Shankara Prana Vallabhe
Gnana Vairagya Sidhyartham
Biksham Dehi cha Parvati
Matha Cha Parvathi devi, pita devo maheshwarah
Bhandava Shiva Bhaktas Cha,
Swadesho Bhuvana Trayam.
Annapoorne - the wife of Lord Shiva; She who is full of food; Sadapoorne - who is always full of resources; Sankara - of Lord Sankara(Shiva); Prana - the life-force; energy; Vallabhe - the beloved; Jnana - knowledge; Vairagya - attitude of renunciation; Siddhyartham - to fulfill the purpose of; Bhiksham - alms, food; Dehi - giveus; Namostute - we bow down to You
O Annapurna, Who art ever full, the beloved life-force of Lord Sankara (Shive, O' Parvathi - grant me alms that I be firmly established in Knowledge and Renunciation. Mother is shakti, father is shiva, relatives are the devotees of shiva and own country is all the three worlds.

2. Bhojana Shlokam from Bhagavadgeetha 4:24
BrahmaarpaNam brahma havir
Brahmaagnaou brahmaNa aahutam
Brahmaiva tEna gantavyam
Brahma karma samaadhinaa
Aham Vaishvaanaro Bhutva
Praaninaam Dehamaashritha
Praanaapaana Samaa Yuktaha
Pachaamyannam Chatur Vidam
The offering is to Brahma, that what is offered is Brahma, Brahma is the fire that consumes, and the entire process is itself Brahma I, the Supreme Spirit, abiding in the body of living beings as the Fire (Vaiswanara) in their stomach I am associated with their Praana and Apaana, digest the four type of foods (solids, fluids, semi-fluid and liquid) which they eat.

3. Bhojana Shlokam from Moh Mudgar(Bhaja Govindam) written by Sri Adi Shankracharya
Punarapi jananam punarapi maranam
punnarapi jannijatthre shanayam
Iha samsaarae bahudhusthaarae
Krupayaaparae paahi murarae
Repeated births, repeated deaths, and repeatedly laying in the mother's womb
It is very difficult to cross this world (to be liberated), shower endless grace on me Murari.

4. భోజన పూర్వ శ్లోకం
బ్రహ్మార్పణం బ్రహ్మ హవిః బ్రహ్మాగ్నౌ బ్రహ్మణాహుతమ్ |బ్రహ్మైవ తేన గంతవ్యం బ్రహ్మ కర్మ సమాధినః ||
అహం వైశ్వానరో భూత్వా ప్రాణినాం దేహ-మాశ్రితః |ప్రాణాపాన సమాయుక్తః పచామ్యన్నం చతుర్విధమ్ ||
త్వదీయం వస్తు గోవింద తుభ్యమేవ సమర్పయే |గృహాణ సుముఖో భూత్వా ప్రసీద పరమేశ్వర ||

భోజనానంతర శ్లోకం
అగస్త్యం వైనతేయం చ శమీం చ బడబాలనమ్ |
ఆహార పరిణామార్థం స్మరామి చ వృకోదరమ్ ||
One may repeat one or all above of these shlokas given above. Usually while saying these mantras the person also takes a little water in his hand and as he repeats these mantras, he sprinkles on food, and clockwise a little water around his plate while chanting antharyAmine namah, in order to do nivedyam to the God who resides in you. This is to bless the food with the power of the mantras.

Then perform the following prANAhoothi. Use only the thumb, index finger and middle finger of the right hand and take a very little amount of the rice and ghee mixed and swallow it without touching the teeth.
Om prANAya svAhA (east)
Om apAnAya svAhA (south)
Om vyAnAya svAhA (west)
Om udhAnAya svAhA (north)
Om samAnAya svAhA (center)
Om bhrahmaNE svAhA (center)


One can say any number of times SriGovindhAya nama: while eating food.

One may display Kamadhenu mudra(also known as Surabhi Mudra also helps to improve the functioning of the digestive system and helps provide relief from stomach ailments).

Now go ahead start eating without talking.

ORDER OF REPEATING THE MANTRAS:
If one practices mantrayog one must first remember the Guru(Shri Adi Shankaracharya, if you don't have a formal Guru), then Ganesh, then Bhairav, then Lord Shiv and finally the divine mother.

BHOJANA (taking meals):
Dress:
One should take his meals in a clean state, with peaceful mind.
One may wear prasada garlands of the Lord and sandalwood paste.
The grihastha may wear rings on his fingers.
One should wear two pieces of cloth.
Ones cloth should not be damp.
One should not have ones head covered.
One should not be wearing shoes.
Five parts of the body should be damp (washed with water): two hands, two feet, and the mouth.

Place:
One should eat in a place which is clean and spacious.one should not eat in a vehicle.
One should sit on an asana, but the asana should not be broken.
One should sit with legs crossed, not spread out.
One should not receive foods directly in the hands and place it in the mouth, nor place food directly on the floor, but should take his meal from a plate.
One should not eat off a broken plate.
One should not keep the plate on the lap.

Direction:
One should sit facing east, or north, according to the Vishnu Purana.
E - By eating facing east, ones duration of life increases;
S - by eating while facing south one gains fame;
W - by eating facing west one gains wealth;
N - and by facing north all of ones desires are fulfilled (Kurma Purana).
Or one may face in the direction of the sun.
One should not face northeast, northwest, southeast or southwest.

Time:
One should not eat at the sandhyas: sunrise, noon and sunset.
One should not eat until food form the previous meal has digested.
One should not eat before having performed sandhya vandana (chanting gayatri at the sandhya) or daily morning puja.
One should not eat for four praharas before an eclipse of the sun or three praharas before an eclipse of the moon.

Sitting Arrangement;
Those of similar rank should sit in the same row.
According to the rules, the moment one person in a row finishes his meal and rises to go, the meal has ended, and the rest of the people in the row are forbidden to continue eating. All of the remaining food is considered ucchista (leftovers) and untouchable. Therefore, out of respect, all persons in the row should wait for the senior ranking person in the row to finish before rising to go. When the senior person rises, then all others in the same row should also rise and leave.
The senior person may sit separately, so that he is not affected by anyone else rising and leaving.

Respects:
Mahaprasad is nondifferent from God. Therefore instead of eating mahaprasada one should honor it. It is said here, karila vandana ...he offered prayers. When taking mahaprasada one should not consider the food ordinary preparations. One should consider mahaprasad a favor of God.  Before beginning the meal, one should glance over the prasadam and pay ones respects to it remembering that it is he mercy of the Lord.  One should always seek the permission of the Lord to act or eat or speak and by the blessing of the Lord everything done by devotee is beyond the principle of the four defects typical of the conditioned soul.